1. Field of the Invention
The present invention relates to a cylindrical dynamic damper that is mounted on hollow or solid rod shaped members such as a variety of shafts, arms and pipes, which are excited by means of vibration transmitting therethrough, and that is able to damp vibrations excited in the rod shaped vibrating member.
2. Description of the Related Art
A variety of rod shaped members including power transmitting members such as shaft and arms as well as pipes forming fluid passages are likely to cause problems of resonance themselves and vibration transmission therethrough. One of the known measures for these problems is a dynamic damper that is mounted on the rod shaped member.
JP-Y-2-18363 discloses one example of the dynamic damper wherein a cylindrical fastening member and a mass member are arranged in a concentric fashion, and elastically connected together by means of elastic connecting members formed of elastic body. The cylindrical fastening member is disposed about and fitted onto the rod shaped vibrating member so that the mass member is elastically supported on the rod shaped vibrating member via the elastic connecting members, thereby providing a secondary vibrating system with respect to the primary vibrating system of the rod shape vibrating member. This type of dynamic damper, for example, has been applied to an automotive drive shaft or the like.
In the dynamic damper as disclosed in JP-Y-2-18363, for example, a plurality of elastic connecting members are spaced away from one another in the circumferential direction, and a plurality of elastic film members of film shape are disposed between adjacent ones of elastic connecting members, respectively. That is, circumferential spacings between adjacent ones of the elastic connecting members are closed by means of these elastic film members, making it possible to prevent entry of the pebbles or the like into the gap between the elastic connecting members. Further, the presence of the circumferential spacing between adjacent ones of the elastic connecting members may pose the problem of burrs irregularly formed at around the parting line of a mold where mold halves faces are mated together. These burrs may cause deterioration in damping characteristics and/or durability of the dynamic damper. Forming the elastic film members is able to eliminate the presence of the parting line of the mold between adjacent ones of the elastic connecting members, thereby preventing deterioration in damping characteristics caused by the burs irregularly formed at around the parting line.
However, in the dynamic damper disclosed in JP-Y-2-18363, the elastic film members are likely to undergo compression/tensile deformation in accordance with the displacement of the mass member in the input direction of vibration to be damped. As a result, the elastic film members are prone to give an adverse effect against the spring constant of the secondary vibration system, even if these are made thin. Also, this makes it difficult to make a spring component in the secondary vibration system composed of the dynamic damper small, limiting a freedom in tuning the secondary vibration system. Further, a slight variation in the wall thickness of the elastic film members may cause a variation of the tuning frequency of the secondary vibration system, so that the dynamic damper may not provide a desired damping performance effectively.
To cope with this problem, the present assignee has been proposed in JP-A-8-277883 the improved dynamic damper wherein the elastic film members are formed in a bellows shape or an inclined plane shape, so that the elastic film members undergo shear deformation upon displacement of the mass member with respect to the rod shaped vibrating member in the axis-perpendicular direction. This improved dynamic damper is able to minimize adverse influence of the elastic film member on the spring constant of the secondary vibration system and the vibration damping characteristics of the dynamic damper during relative displacement between the mass member and the rod shaped vibrating member in the axis-perpendicular direction.
However, the extensive studies conducted by the present inventor have revealed that the dynamic damper disclosed in JP-A-8-277883 has still some room for improvement. Namely, with respect to the elastic film members of bellows like shape, if the radial distance between the cylindrical fastening member (or the rod shaped vibrating member) and the mass member is not large enough, upon input of large vibrational load, the elastic film members are folded up, possibly causing significant increase in the spring constant of the secondary vibration system. Furthermore, if the radial distance between the cylindrical fastening member and the mass member is made large enough, it becomes difficult to meet sufficiently the small-sizing requirement on the other hand. Thus, it might become difficult to employ the dynamic damper of construction as disclosed in JP-A-8-277883 depending on a kind of input vibration and/or a required space for installation.
With respect to the elastic film members of inclined plane shape, though the increase in the spring constant due to folded elastic film members can be avoided, the inclined elastic film members will cause a slant of an elastic principal axis of the spring component of the dynamic damper with respect to the axis-perpendicular direction that is the vibration input direction. Accordingly, the mass member is likely to cause swinging displacement in a prizing or twisting direction upon input of vibration, so that the undesirable displacement of the mass member in the directions except in the vibration input direction may possibly deteriorate desired vibration damping effect of the dynamic damper.